This application is based on Application No. MI2006A 002161 filed in Italy on Nov. 10, 2006, the content of which is incorporated hereinto by reference.
The present invention relates to a three-pole electric apparatus, in particular for medium or high voltage electric substations. For each pole, the apparatus comprises an air-insulated disconnector able to perform line isolating functions and a circuit-breaker using the technique of vacuum circuit-breaking in order to perform line protection functions. The apparatus according to the invention is suitable for installation in cubicles of the protected type which form medium or high voltage electric switchboards. These cubicles also contain an air-insulated earthing switch able to perform line earthing functions.
As is known, an electric switchboard represents all the electrical apparatus situated in a node of the electrical network, the purpose of which is to transmit or concentrate the electric power in order to allow efficient transportation and/or distribution thereof. Generally, in a node there are one or more lines which converge there and several lines which depart therefrom. Generally, the regulations for medium and high voltage apparatus envisage that, in a node of the network, each incoming and outgoing line is provided with apparatus which perform isolating and earthing functions (to ensure safety) and a protective function (to allow the elimination of faults which may arise).
A circuit breaker is able to protect the line leaving the node and directed towards the user. A disconnector, after the circuit breaker has opened the line leaving the node and directed towards a user, is able to disconnect physically this line. Finally, an earthing switch, provided that the disconnector has disconnected the line from the node which supplies or receives the voltage, earths the line so as to allow the operator to access in complete safety the conductors which are normally live. All of the abovementioned devices, situated in a node of the network, in addition to other devices not relevant for the purposes of the present invention, present in an electric power distribution node, are generally referred to by the term “switchboard”. Each switchboard is composed of several cubicles inside which the circuit-breaking, isolating and earthing functions for each line are performed.
EP 1,226,596 in the name of the same Applicant describes a three-pole apparatus for electric substations which has an extremely compact structure compared to the known apparatus. The device according to EP 1,226,596 comprises a series of isolators which contain at least one disconnector, a circuit breaker and an earthing switch. The circuit breaker is sealed inside a vacuum bulb and is positioned in series with a line-earth disconnector device which is movable between a first position where it connects said circuit breaker to a contact of the voltage busbars and a second position where it connects the circuit breaker to an earth contact. According to EP 1,226,596, the line-earth disconnector and the circuit breaker are all contained inside a metal casing and the isolators are arranged at the input and output terminals of the device.
The abovementioned known device is extremely compact, efficient, safe and reliable. However, the Applicant has set itself the aim of providing a three-pole apparatus, typically for a medium or high voltage cubicle, comprising, for each pole of the apparatus, a disconnector able to perform line isolating functions and a circuit breaker able to perform circuit-breaking functions, which apparatus can be easily extracted from the cubicle in complete safety by the maintenance personnel. Rapidity and ease of extraction are of primary importance for keeping the intervention times to a minimum. Safety for the operators is also an indispensable feature for this type of apparatus.
EP 0 543 683 discloses a multipole load break switch comprising, for each pole, an insulating bushing enclosing an evacuated bulb, the bushing including at a first end a first contact connected to a first terminal of the bulb and intended to cooperate with a first conductor, and at a second end a second contact connected to a second terminal of the bulb and intended to cooperate with a second conductor, the bushings being integral with a common metal section shrouding a common shaft for operating the bulbs and which is actuated by a mechanism contained in a cabinet integral with the section.